Proceed north to the casino and talk to the girl in red for another cutscene, choose the top option when talking("yes") and Tsuki will follow you. proceed sotuh on area and go 2 areas west and enter the second building on the right side(north) and a cutscene will happen, picture of this building is below.

the house you need to enter is on the left, where you would enter this specific area is the gate on the right side of the picture.Watch Jiraia be an idiot to the weird blue thing(Takoumaru) and after it ends Takoumaru is also following you. head back to the casino and walk near its front door for another cutscene and tsuki will open a secret door. once in go to the next area and exit through the door, there are stairs to the north go up them. then go south for another cutscene, after it ends go south for another set of stairs. Go north for another cutscene. After it ends you will gain an item(tsuki no namida), and another cutscene will start and once that ends you will get this achievement and Orochimaru will rejoin your party.